1. Field of the Invention
The present invention relates to a power supply control system which controls a power supply voltage supplied from a power supply unit to a load circuit.
2. Description of the Related Art
In recent years, a digital camera and digital video camera are becoming prevalent as image capture apparatuses. These cameras form an image of light from an object on an image capture element via an optical lens, thereby capturing and recording a digital image of the object. Such image capture apparatuses include a power supply control system which controls power supply voltages supplied to load circuits such as a circuit for driving the optical lens and that for operating the image capture element (see Japanese Patent Laid-Open No. 7-288930).
Japanese Patent Laid-Open No. 7-288930 discloses a power supply control system in which a fuse is inserted in a power supply line which supplies power supply voltages (DC voltages) from a power supply circuit (DC-DC converter) to a plurality of load circuits. When an overcurrent flows into the power supply line as the load circuit, DC-DC converter, or the like short-circuits, such a power supply control system disconnects the power supply line by the fuse so that the supply of a power supply voltage to the short-circuited device can be stopped without any influence such as voltage fluctuation on the other load circuits.
A power supply control system as shown in FIG. 3 has also been known. FIG. 3 is a schematic block diagram showing the configuration of a conventional power supply control system 1000. In FIG. 3, a power supply unit 1010 includes a battery, and a power supply circuit 1020 includes a DC-DC converter. DC voltages output from the power supply circuit 1020 are applied to load circuits 1070, 1080, and 1090 as DC power supply voltages for operating them. A current detection resistance 1040 and current limiting resistance 1050 are connected in series with each other between the power supply unit 1010 and the power supply circuit 1020.
The two ends of the current detection resistance 1040 are connected to a current determination circuit 1032 included in a control unit 1030. The control unit 1030 includes a control circuit 1034 which receives the output from the current determination circuit 1032. The operating power supply voltage of the control unit 1030 is directly supplied from the power supply unit 1010. A shutoff switch (SW) circuit 1060 is connected in parallel with a current limiting resistance 1050. The shutoff switch circuit 1060 is controlled in accordance with a control signal from the control circuit 1034. The control signal from the control circuit 1034 is also supplied to the power supply circuit 1020, and used to control the power supply circuit 1020 to an operative state.
However, the power supply control system requires a large consumption current in operation, so the consumption current of the power supply control system is preferably minimized when the image capture apparatus is not used.
A general image capture apparatus has a battery lid to prevent detachment of a battery serving as a power supply. Even while the battery lid is open, a power supply voltage is often supplied to the image capture apparatus as long as the battery is attached to the image capture apparatus. In this case, the power supply control system is in a sleep state while the battery lid is open. However, because an abnormal current cannot be monitored while the power supply control system is in a sleep state, a fuse must be inserted in the power supply line. Once the fuse blows out, it must be replaced with a new one. It is difficult and inconvenient to replace a fuse in a compact apparatus such as an image capture apparatus. However, when the power supply control system is always kept in a normal state, it wastefully consumes the power of the battery.